It is well known in the art to use motion detecting systems for controlling actuation of other devices, such as an alarm device connected thereto, in response to a motion of an object to which the motion detecting system is attached or of the system itself. In this fashion, the owner of the object or system can be alerted by an alarm emitted by the alarm device when the object or system is moved, which may suggest an attempt at theft or tampering with the object or system.
In order to detect such motion, many such motion detecting systems use magnets or magnetic devices. Typically, such motion causes a corresponding motion of the magnet or magnetic device, whose magnetic field causes an electrical contact to open or close, which, in turn, causes a signal or electric current to be transmitted to the alarm device. The electric current or signal then causes the alarm device to actuate and emit an alarm.
An example of such a system is described in U.S. Pat. No. 4,275,291, issued to Okamura on Jun. 23, 1981, which discloses a portable alarm device having a motion detecting system that senses motion of the alarm device corresponding to a motion of the object to which the alarm device, including the motion detecting system, is attached. The motion detecting system includes a pendulum with attached magnet, set in motion by motion of the alarm device, which causes closing of alarm circuit reed switches to actuate a continuous alarm. However, disadvantageously, the alarm device requires use of a key to disable the alarm while placing the alarm device on the object to ensure that the alarm device is not actuated during placement and arming of the alarm device.
Obviously, should the key be lost or damaged, operation and utility of the alarm device will be compromised as authorized motion of the object and/or alarm device, i.e. motion caused by a legitimate user or owner, will cause the alarm device to emit an alarm.
U.S. Pat. No. 4,888,986, issued to Baer et al. on Dec. 26, 1989, discloses a rotational position indicator having nine position sensors substantially equally spaced around the circumference of a circle and. an armature mounted for rotation on an axis located at the center of the circle. The armature is formed with two position magnets for activating the sensors mounted on arms of the armature at approximately one hundred and forty degrees relative to each other. Each magnet is mounted at a radial position for selectively actuating the position sensors upon rotation of the armature. An electric circuit is coupled to each position sensor for indicating actuation or not of the respective position sensor. The output provides a unique position code for successive intervals of angular positioning of the armature. The actuators have an actuating effect over a selected angular interval sufficient to produce thirty-six unique position codes for identifying successive ten degree intervals of angular positioning of the armature relative to the stator. By detecting changes in position, the indicator may detect motion. This position indicator, however, is needlessly complex for purposes of motion detecting for an alarm device, as, for such purposes, exact position need not be known. Rather, only changes in position, i.e. motion, need be detected to actuate the alarm device. Also, disadvantageously, since the detector only recognizes thirty-six positions representing ten degree arcs, changes in position in between any two adjacent positions of the thirty-six positions may be undetected. In such circumstances, problems may also arise in determining which position will be considered for initializing, i.e. arming, the system.
U.S. Pat. No. 4,012,611, issued to Petersen on Mar. 15, 1977, teaches an intrusion alarm device in which the motion detecting system comprises a body of predetermined mass suspended in pendulum-like fashion upon a rod or the like from a fixed point within a housing. A switch arrangement including a magnetically actuatable switch, with overlapping contacts, and a magnet is mounted with respect to the end portion of the rod and a fixed, null location upon the housing. Any relative movement between these components will activate a digital circuit which will activate the alarm device and sound an alarm. While the overlapping of the contacts helps bias the rod towards the null location in which the system is in an armed state, and thus resolves some of the difficulties related to arming the motion detecting system, it also requires, disadvantageously, use of relatively complex logic and relatively complex logic circuits.
Accordingly, there is a need for a simple, portable, and self-contained motion detecting system which is capable of being easily and consistently set in an armed state for arming the system.